1. Field of the Invention
The present invention relates generally to a shift control apparatus in an automatic transmission mounted in an automobile, and more particularly to an apparatus for controlling shifting when driven wheels of the automobile slip.
2. Description of Related Art
Conventionally, a shift control apparatus for an automatic transmission for shifting from a low gear stage to a high gear stage when driven wheels of an automobile slip during take-off, is disclosed in the publication of JPA SHO 60-176828. According to this art, when the driven wheels slip on a road with a low friction surface, such as a wet or icy road, a sensor and the like detects that slip and outputs a slip signal to a shift control apparatus for an automatic transmission. The shift control apparatus then receives the slip signal and performs shift control to shift the automatic transmission from a low gear stage with a large transfer torque to a high gear stage with a small transfer torque. This decreases the driving force transmitted to the driven wheels and thereby prevents continued slipping.
With this shift control apparatus for an automatic transmission, however, when slip of the driven wheels is detected, the shift control apparatus immediately performs shift control to shift the automatic transmission into a high gear so that even when the driven wheels slip on a normal road, which is not a road with a low friction surface as described above, or so-called wheel spin occurs temporarily, the shift control is performed to shift the automatic transmission into a high gear stage. Because of this, even if temporary wheel spin stops thereafter such that the driven wheels are no longer slipping, the automobile temporarily runs in a high gear stage with low torque against the will of the driver, thereby giving the driver and other occupants a sense of discomfort and making the necessary driving force unable to be achieved.
Therefore, it is an object of the present invention to provide a shift control apparatus for an automatic transmission which eliminates or reduces the sense of discomfort felt by the driver and other occupants and which is able to achieve the necessary driving force when slip occurs, particularly during take-off.